Chelation and Performance Enhancement Mechanisms of Ester-Modified Triethanolamine in Cement-Based Materials

Abstract

Adding triethanolamine (TEA) as hardening accelerator is one of the most effective ways to improve cement hydration rate and strength, but its early strength effect is limited and potentially compromises the late-stage cement strength. In view of this, an ester-modified triethanolamine (TG) was conducted, and its effects on cement hydration and mechanical properties were investigated based on chelation theory and hydration mechanisms. Results showed that the formation of ester groups enhanced the hydrophobicity and fluidity of cement paste and extended the setting time. The retained amino and phenolic hydroxyl groups in TG enabled selective coordination with Ca2+, Al3+ and Fe3+, effectively regulating the dissolution-precipitation behavior of ions in cement pastes. Compared to TEA, TG exhibited high chelating ability, with increases of 142.2%, 29.9%, and 82.8% for Fe3+, Al3+, and Ca2+, respectively. Furthermore, the incorporation of TG resulted in larger impedance arcs in the Nyquist curves and increased gel and mesopore volumes by 14.6% and 8.4%, respectively. TG-0.05% improved 28-day compressive strength by 17.1% and 36.6% compared to the Control and TEA-0.05% groups. However, excessive TG (1.0%) weakened the selectivity and thermal stability of the hydration process by forming a dense organic film, increasing the residual C3S and C2S contents, and causing abnormal CH accumulation as well as undesired carbonation and impurity phase formation. This study provides new insights into the molecular-level design of multifunctional alkanolamine-based admixtures and offer a tunable strategy for regulating cement hydration and microstructure through targeted chelation.

Keywords: Cement, Triethanolamine, Ester modification, Chelation effect, Hydration